I. Field of the Invention
The present disclosure relates generally to the fields of chemistry and materials science. More particularly, it concerns metal nanoparticles having an epoxide-based oligomer coating, compositions thereof, method of making the same, and methods of use thereof, including for energy related applications.
II. Description of Related Art
Aluminum nanostructures are valuable for many energy-related applications. These applications stem from aluminum's low atomic number, low density, high abundance, low cost, and its 3 electron reduction and high redox potential. Micron-sized aluminum particles have long been used in thermite reactions, as propellants for rockets, in magnetohydrodynamic generators, and other applications. Aluminum's advantage over comparable organic solids as propellants is its high energy density. In addition to the long history of aluminum as a solid propellant, it has also recently been discussed as an additive to liquid fuels. Phelan and coworkers recently demonstrated that nanoscale aluminum increases the ignition probability of diesel fuels (Tyagi et al., 2008). Further, nano aluminum and alanates are being considered as hydrogen storage materials (Baldé et al., 2006.
While there are many applications for nanoscale aluminum materials there are challenges with producing air stable nanoscale aluminum structures with small diameters (<100 nm). Buhro demonstrated that unprotected aluminum nanostructures are kinetically unstable to grain growth (Haber and Buhro, 1998). Aluminum is also reactive with oxygen and water to produce Al2O3 to give a 2-6 nm thick oxide layer (Aumann et al., 1995). This layer passivates the underlying aluminum core, but it is a significant fraction of the mass of small nanostructures. For nanoparticles with diameters less than 20 nm the oxide layer can account for more than 70% of the particle mass. This oxide layer significantly lowers the nanoparticle's energy density, slows the nanoparticle combustion rate, may prevent complete aluminum consumption, and can reduce hydrogen absorption for storage applications. Accordingly, identifying and developing materials and compositions that overcome these limitations is desirable.
A number of passivation strategies have been reported for aluminum nanoparticles. For micron-sized particles, simple oxide passivation may be useful since an oxide coating of a few nanometers accounts for only a few percent or less of the total particle mass. For larger particles, alternatives to oxide passivation of aluminum that provide increased energy content include graphite (Ermoline et al., 2002), polymer (Roy et al., 2004), or transition metal coatings. For nanoscale particles, Jouet and coworkers (Jouet et al., 2005) reported nano-Al stabilization with carboxylic acid monolayer coatings while Foley and coworkers (Foley et al., 2005) reported effective transition metal capping of nano-aluminum. Additional metal coating and passivation techniques would be a great advantage.